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Will an anti-viral drug put paid to measles?

By Debora MacKenzie

TO PROTECT yourself from most viruses, you need to be vaccinated before you catch them. Once you’ve been infected by a virus, there are very few drugs that can attack it. But a drug now promises to battle the measles virus in much the same way that antibiotics fight bacteria.

In addition, this month the first case of a vaccinated person spreading the virus was reported. Public health officials who uncovered the case in New York City speculate that it may have happened because the battle against measles has been so effective. Vaccinated people can need boosters to remain immune. When measles was common, exposure to people with measles acted as a booster – but now it is relatively rare.

An antiviral drug could fight the disease in people who have been exposed but are not vaccinated or have lost immunity. It could also keep them from spreading the virus. Such a drug may now be within reach. Called ERDRP-0519, it was discovered in 2007 by Richard Plemper of Emory University in Atlanta, Georgia, and his colleagues. The drug blocks an enzyme vital to the virus’s replication.

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However, there’s a flaw. In lab tests, ERDRP-0519 protected ferrets that had been infected with a measles-like virus. But animals given the drug just before they got the virus died two weeks after drug therapy ended. Tests suggest that the drug stopped the virus replicating so completely that the ferret immune systems weren’t able to develop immunity to it, leaving them vulnerable to remaining virus once treatment stopped (Science Translational Medicine, doi.org/sdt).

This means that to work in people, the drug will have to be given after someone has been exposed, but before the onset of symptoms. This can take two weeks, so there should be time to treat all the social contacts of someone who has developed measles. After symptoms start, the virus has stopped replicating and so the drug can’t help. But people treated too early might be as vulnerable as the ferrets treated just before infection.

Another potential pitfall is that using an antiviral drug might lead to measles viruses developing resistance to the drug, much as bacteria can become resistant to antibiotics. This could be tragic if resistant strains were also deadlier. Initial tests by Plemper’s team suggest that any such mutants are likely to be less transmissible or virulent than natural measles. Nevertheless, he says any use of the drug should be strictly monitored.

It is also possible that an antiviral drug would encourage people to reject vaccination. This would defeat the whole point, says Plemper. “Measles eradication must by driven by vaccination,” he says. “We developed this drug to rapidly suppress local outbreaks in populations with good vaccination coverage.” That way, the drug can plug gaps in vaccination. “Combined, they may one day succeed in eradicating measles,” he says.

This article appeared in print under the headline “Antiviral could call time on measles”